The objective of this study is to follow, through the first year, one hundred infants seen previously in our newborn laboratory for sensory and habituation studies, and for tests of avidity and defensiveness. Avidity refers to the zest with which the infants suck, and the extent to which their oral behaviors are altered by the sweetness of the fluid for which they suck (expressed as procedures for a "hedonic index"). Defensiveness refers to the strength of response the infant manifests to mildly aversive stimulation such as is routinely encountered under natural conditions. The focus of interest in this study will be on whether there are enduring attributes, centering on approach and avoidance behaviors, through the first year. To explore whether these neonatal behaviors are related to developmental outcomes, we will study these infants at four months and one year of age, using techniques already worked out, and others to be devised, for the study of sensory responsivity, habituation, learning, and wariness. Neonatal responsivity is not perfectly predictive of any known behavioral, psychophysiological, or other developmental outcomes at one year of age. We do not anticipate that the present study will establish a high degree of linear predictivity. Rather, we view this study as the beginning of a longitudinal approach to the study of multiple determinants of developmental outcomes. Some of those determinants, in collaboration with environmental features, are perhaps detectable very early, especially those relating to hedonic responsivity.